Quaternary ammonium compounds are well known for their use in fabric softening applications. It has been found that the quaternary ammonium fabric softening materials comprised of one or more C.sub.8 -C.sub.28 alkyl or alkenyl groups connected to the softener molecule via an ester linkage are of particular importance because they are more biodegradable than conventional quaternary ammonium compounds. It is also known that fatty groups of C.sub.16 to C.sub.18 or longer are necessary to obtain optimum softening in these molecules.
These compounds can be prepared by a number of methods. For example, U.S. Pat. No. 4,515,723 discloses quaternary N-alkyl-N,N',N'-polyoxyalkyl-.alpha.,.omega.-diamino-alkylene fatty acid esters which are prepared by esterifying oxyalkylated fatty alkyl-alkylene diamines and quaternizing the reaction product with an alkylating agent. The quaternization disclosed therein can be carried out in water, in a solvent or without any solvent.
U.S. Pat. No. 4,228,096 claims a method of preparing quaternary ammonium salts from various morpholinones using, among others, dimethylsulfate as a quaternizing agent. This is a two step process in which the quaternization can be conducted either neat or in the presence of an inert solvent. The patent notes however that the quaternization step, V, is preferably conducted in the presence of a polar solvent such as tetrahydrofuran.
European Patent Application EP 0375029 to Procter & Gamble discloses process for preparing substituted imidazoline fabric conditioning compounds and is incorporated in it entirety by reference herein.
PCT Application WO 91/01295 to Truis, et al discloses a process for preparing quaternary ammonium compounds as fabric softeners.
It is an object of this invention to provide a solvent free process for the preparation of certain quaternary ammonium methyl sulfates.
The advantage of this novel process lies in both its economic and environmental importance. Without the use of solvent, the process is clearly less expensive than similar solvent requiring processes. Additionally, no waste solvent is generated with the requisite cost of cleanup or recycling. A further advantage to this solvent-free process is that for certain applications, the use of solvent free material is highly desirable and imparts special value to the end product. Still a further advantage of this process is that it reduces or eliminates the number of undesirable side reactions, such as transesterification, hydrolysis and/or methylation of solvent with the dimethylsulfate. Lastly, an additional advantage lies in the fact that the absence of solvent in the end product reduces or eliminates problems with flammability and/or toxicity associated with lower alkanol solvents such as ethanol, methanol or isopropanol.